One day, a young giraffe arrives in Jomb from the south. The native animals — wild cattle, hippopotami, and ostriches — are amazed and alarmed: they have never seen such a creature before. But Umpo, as the giraffe calls himself, disarms their suspicions with his jolly personality, and soon wins their permission to stay in Jomb. He must obey the local laws, of course; most critically, he must never eat from or otherwise molest the lucky mimosa tree. This comes as a surprise to Umpo, for like all giraffes he is very fond of mimosa leaves; but he agrees.
There is one shadow in this sunny picture; Slythe the Red Panther lives in the forest of Jomb, and does not take to Umpo as the other residents do. In fact, Slythe develops an almost obsessive desire to eat the giraffe. One day, the panther raises an alarm among the animals of Jomb: the lucky mimosa tree has been stripped of its leaves and branches, and Slythe claims to know that Umpo is the criminal. A mob of animals sets out to apprehend him.
(Just before they do, Umpo hears a warning voice speak to him from out of thin air. The voice returns to him in the crisis that follows, guiding him; and Umpo realizes that he is being safeguarded by giraffe-fairies.)
The animals surround Umpo, and Slythe leads the effort to put him to death for his "crime." Umpo both claims and acts like he is innocent, disturbing some of the others; then, remarkably, he agrees to be executed by Slythe. He leads the party into the forest to seek an appropriate spot — and in so doing he finds the place where Slythe has hidden the mimosa branches and leaves that he had stripped from the tree. The animals join to wreak their revenge upon the panther. (After being trampled by a hippo, there is little left of him.)
The animals are amazed to see that the damage to the lucky mimosa is magically restored. They all realize that Umpo is favored by the fairies of his race.